This application relates generally to electrical power generation and, more specifically, to methods, systems, and computer program products for use in adjusting the power output therefrom.
A wind farm, or wind park, includes a group of wind turbines that operate collectively as a power plant that generates a power output to a power grid. Wind turbines can be used to produce electrical energy without the necessity of fossil fuels. Generally, a wind turbine is a rotating machine that converts the kinetic energy of the wind into mechanical energy and the mechanical energy subsequently into electrical power. Conventional horizontal-axis wind turbines include a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle by a shaft. A generator, which is housed inside the nacelle, is coupled by the shaft with the rotor. Wind currents activate the rotor, which transfers torque to the generator. The generator produces electrical power that is eventually output to the power grid.
Due to the natural intermittency of wind as well as outages that occur when a transmission line from a wind turbine or the wind turbine itself fails, the power output from a particular wind turbine or wind farm is less consistent than the power output from conventional fossil fuel-fired power plants. As a result, the power from wind turbines operating at nominal conditions in a wind farm may not meet output requirements for the power grid, resulting in decreasing frequency of the power grid. For example, the power from the wind power plant often will not track the forecasted power due to wind forecast, transmission line, or wind turbine errors. As another example, the rate of change of power for a wind power plant may be outside of a desired range because of wind gusts. A conventional approach for dealing with these and other similar situations is to use wind turbine controls to manage the operation of the wind farm, such as utilizing pitch control of the rotor blades to increase or decrease, within some limits, the power produced by the individual wind turbines, as well as using a braking system to decrease, within some limits, the power produced by the individual wind turbines.
Moreover, due to loads being added and withdrawn to the power grid, the power output from a particular wind turbine or wind farm needs to be adjusted to maintain the power grid at its nominal ranges for power and frequency, to name some examples. As a result, the power from wind turbines may not meet output requirements for the power grid. For example, a load may be added to the power grid and result in decreasing frequency of the power grid. On the other hand, a sudden withdrawal of a load may result in increasing frequency of the power grid. Although some conventional systems simply result to load shedding (to increase the frequency of the power grid if it decreases beyond a predetermined threshold) or generator shedding (to decrease the frequency of the power grid if it increases beyond another predetermined threshold), a more conventional approach for dealing with these and other similar situations is to again use wind turbine controls to manage the operation of the wind farm, such as utilizing pitch control of the rotor blades to increase or decrease, within some limits, the power produced by the individual wind turbines.
As such, wind turbines are operated in a curtailed mode. In the curtailed mode, the wind turbines are not generating all the power available from the wind or otherwise available. The difference between the power being generated and the maximum power available, or “control margin,” may be fairly wide, such as about 0.5 MW wide, and used for emergency additional power output.
An increase or decrease in the frequency of a power grid often occurs in fractions of a second. Changing the pitch of the blades to adjust the operation of the wind turbine in the curtailed mode often takes no less than seconds, as there is a delay associated with determining or otherwise communicating a command to a wind turbine to adjust the pitch of the blades as well as a delay for any pitch adjustment mechanisms to actually change the pitch of the blades. Furthermore, there is a delay associated with the increase or decrease in speed of the blades of the wind turbine in response to the adjustment of the pitch of the blades, and thus a delay when the actual power output of a wind turbine increases or decreases. Moreover, operating a wind turbine in a curtailed mode necessarily results in the wind turbine producing less power than that which would be available. Specifically, the curtailed mode may require that brakes be applied to the wind turbine to maintain the power generation within the middle of the control margin. Still further, the operation of the wind turbines at slower than capable speeds often increases the stress on the blades, rotors, and other mechanical components of the wind turbines. This results in increased wear on wind turbine components as well as increased costs for maintenance, replacement, and operation.
Improved methods, systems, and computer program products are needed for coordinating the generation of power by wind turbines in a wind farm.